Three-Dimensional Motion of Sliders Contacting Media

[+] Author and Article Information
James Kiely, Yiao-Tee Hsia

 Seagate Technology, 1251 Waterfront Place, Pittsburgh, PA 15222

J. Tribol 128(3), 525-533 (Mar 07, 2006) (9 pages) doi:10.1115/1.2194914 History: Received February 01, 2005; Revised March 07, 2006

Characterization of slider motion induced by contact is becoming a critical aspect of developing advanced head-disk interfaces. While vertical motion induced by contact has been studied, very little is known about off- and down-track motions. We have applied three separate laser Doppler vibrometers to measure slider movement in three orthogonal directions simultaneously. We have measured the position of a slider as it undergoes a transition from flying to making full contact with the media surface. We find that slider motion varies considerably with varying levels of contact and that motion in all three directions is considerable. Spectral decomposition is used to identify the vibration modes that are excited in each direction, and we find that for most of the test velocities, modes excited in the vertical direction give rise to motion in the two orthogonal directions. In addition, we present a depiction of the vertical, down-track, and off-track position changes by plotting the position of the slider in real space coordinates to help visualize more completely how the slider moves in space. These trajectories depict the periodic, elliptical path the slider takes and identify how the paths change with contact. Analysis of motion identifies that at some levels of contact, a majority of motion is repeatable, but that nonrepeatable components increase with the amount of contact. Additionally, down-track motion is the only component whose magnitude increases monotonically with increasing contact.

Copyright © 2006 by American Society of Mechanical Engineers
Topics: Motion , Disks
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Figure 1

Schematic view of the air bearing design used in this study. The main air bearing surfaces are shaded gray.

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Figure 2

The locations of the three LDV beams are depicted by “●”s and are located on the outer diameter side, top, and trailing end of the slider

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Figure 3

Power spectra of slider displacement in three orthogonal directions are shown for five linear velocities, illustrating how displacements change with head-disc contact. In (a), as the slider flies at 26.6m∕s, the only peaks are below 20kHz and are smaller than 0.1nm. As the slider contacts at 23.9m∕s (b), the dominant peak is at 244kHz, which corresponds to a slider pitch mode. The amplitude is largest in the vertical. In (c), at 21.3m∕s, the main peak shifts to 190kHz and is on the order of 1nm in all directions. With increased contact at 16.0m∕s (d), the spectra become more complex, with the main peaks occurring at 50 and 182kHz. In (e), at 10.6m∕s, the displacements are diffusely spread, with displacement components occurring over a wide range of frequencies. Peak magnitudes are larger in the down-track direction than in the vertical.

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Figure 4

Schematic views of the perspectives used to illustrate slider position. (a) The side elevation, in which the down-track direction is the x-axis and the vertical direction is the y-axis. (b) The plan view, in which the down-track direction is the x-axis and the off-track direction is the y-axis. (c) The trailing end elevation, in which the off-track direction is the x-axis and the vertical direction is the y-axis.

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Figure 5

Trajectories of slider motion as it flies without contact at 26.6m∕s viewed from (a) side elevation, (b) plan view, and (c) end elevation. As expected, less than 1nm of perturbation of the slider position is observed. These figures are shown to illustrate that the noise level in the measurements is small and to illustrate the significant increase in slider motion caused by contact.

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Figure 6

Trajectories of slider motion as it makes contact at 23.9m∕s viewed from (a) side elevation, (b) plan view, and (c) end elevation. Motion is larger than at 26.6m∕s and the slider motion is elliptical when viewed from the side elevation. Motion is predominantly vertical. Indicated position changes are with respect to the mean position and not the media surface.

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Figure 7

Trajectories of slider motion as it makes contact at 21.3m∕s viewed from (a) side elevation, (b) plan view, and (c) end elevation. Motion is periodic and, when viewed from the side elevation, the path again appears to be elliptical.

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Figure 8

Trajectories of slider motion as it makes contact at 16.0m∕s seen from (a) side elevation, (b) plan view, and (c) end elevation. The magnitude of motion is considerably larger in all directions and the elliptical paths in the side and end elevations now have considerably more variation.

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Figure 9

Trajectories of slider motion as it makes contact at 10.6m∕s seen from (a) side elevation, (b) plan view, and (c) end elevation. Down-track motion is the largest in magnitude and motion is generally chaotic without a clearly repeatable path.

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Figure 10

Plot of one standard deviation of vertical, off-track, and down-track motion as a function of test velocity. Motion in all three directions is of the same order of magnitude. As the velocity decreases, all motion generally increases in magnitude, but only down-track motion shows a monotonic increase with decreasing velocity.

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Figure 11

Trajectory of the repeatable, harmonic slider paths for 23.9, 21.3, and 16.0m∕s. The repeatable motion is derived from sinusoidal fits to the position data and identifies the repeatable elliptical paths the slider takes as the amount of contact increases.

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Figure 12

Trajectory of the nonrepeatable, aperiodic portion of slider motion for (a) 23.9, (b) 21.3, and (c) 16.0m∕s, obtained by subtracting the repeatable portion of motion (plotted in Fig. 1) from the actual position. The amount of nonrepeatable motion is approximately 2nm for 23.9 and 21.3m∕s, but increases significantly at 16.0m∕s.



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